Method of Making a Retort Container

ABSTRACT

A method is described for making a retort container having one or two metal ends. A heat-sealable material is present on one or both of the container side wall and the/each metal end. The/each metal end is seamed onto the container body, and the resulting container assembly is conveyed on a conveyor adjacent to an induction sealing head and then adjacent to a cooling device. A pressure belt engages the upper end of the container assembly to keep the metal end from coming off the container body during the induction heating and cooling processes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.13/224,651 filed on Sep. 2, 2011, and U.S. patent application Ser. No.13/284,056 filed on Oct. 28, 2011, the entire disclosures of saidapplications being hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present disclosure relates to containers, particularly to containershaving one or two metal ends applied to one or both ends of thecontainer body and crimp-seamed or double-seamed onto the containerbody, and most particularly to such containers used for retortprocessing.

Traditionally, retort containers have been constructed substantially ofmetal. For many decades the standard retort food containers have beenthree-piece or two-piece metal cans. In a three-piece metal can, a metalcan body is closed by a pair of metal ends that are typicallydouble-seamed onto the ends of the can body. A two-piece metal caneliminates one of the metal ends because the can body is a deep-drawnbody with an integral bottom wall. The metal ends of such typical retortcontainers have an outer peripheral portion forming a “curl” thatreceives the end of the can body, and after the end is applied the curland the wall of the can body are rolled up together to form a doubleseam. This construction has the great advantage that it readilywithstands retort processing without the seams being compromised,because the plastically deformed metal of the can body in the seam areatends to hold its deformed shape despite the high pressure andtemperature during retort.

More recently there has been a desire to construct retort containersthat use less metal, motivated by the potential cost reduction andimproved aesthetics that such a construction can offer. The developmentdescribed in the present disclosure at least in some aspects is aimed ataddressing this desire.

BRIEF SUMMARY OF THE INVENTION

In particular, the present disclosure describes a retort containerhaving one or two metal ends attached to a container body in such a waythat there is an improvement in blow-off resistance when the inside ofthe container is pressurized relative to outside ambient pressure forany reason (e.g., during retort processing, or as a result of changes inaltitude of the container, such as when a container is filled and sealedat sea level and is subsequently transported to a high-altitudelocation). The improvement derives from a thermal fusing of the metalend to the container body, as described herein. This could allow thecontainer body to be a thinner metal than typically used for metalretort containers, where the thinner metal would have less resistance to“unrolling” under high internal-pressure conditions, or could allow thecontainer body to be formed of a non-metallic material (e.g., plastic orcomposite), since blow-off resistance is not dependent primarily uponthe ability of the rolled-up container end in the seam being able tohold its deformed shape.

In accordance with the invention in one embodiment, a method of making aretort container comprises the steps of:

-   -   providing a container body having a side wall extending about a        container body axis, the side wall having a lower end and an        upper end, the upper end defining an upper edge that extends        about a top opening of the container body, the side wall having        an inner surface and an outer surface;    -   applying a metal end to the upper end of the container body, the        metal end having at least a metal layer and comprising a central        portion and an outer peripheral portion extending generally        radially outwardly from the central portion and extending        circumferentially about the central portion, the peripheral        portion having a radially outer part and a radially inner part,        a first heat-sealable material being present on at least one        of (a) a lower surface of at least the peripheral portion of the        metal end and (b) the inner surface of the side wall adjacent        the upper end thereof, the radially outer part of the peripheral        portion defining a curl, the radially inner part of the        peripheral portion defining a chuck wall that extends generally        downward from the curl and has a radially outer surface forming        an interface with the inner surface of the side wall of the        container body;    -   forming a seam connecting the metal end to the upper end of the        side wall, the seam having the curl of the metal end and the        upper end of the side wall interlocked, the container body and        seamed metal end constituting a container assembly;    -   disposing the container assembly between a lower conveyor and an        upper pressure belt which cooperatively engage opposite ends of        the container assembly to prevent the metal end from coming off        the container body, and which convey the container assembly        along a path; and    -   induction heating the metal end to melt the first heat-sealable        material and then cooling the first heat-sealable material so as        to fuse the metal end onto the container body, wherein the        heating and cooling steps take place during the engagement of        the conveyor and pressure belt with the container assembly.

Heat-sealable materials useful in the practice of the present inventioncan comprise any known heat-sealable materials. The metal end can havean interior coating, and optionally an exterior coating as well.

The container body can be open at both ends that are each closed by ametal end in accordance with the invention, or can be open at only oneend such that only one metal end is needed. The container body can bemade in various ways. For example, the container body when metal can beformed from sheet metal seamed along a longitudinal seam in the usualway, or can be deep drawn to have an integral bottom wall. When plastic,the container body can be formed by any of blow-molding, thermoforming,or injection-molding so as to have a bottom wall integrally joined tothe side wall, or extruded so as be open at both ends.

In some embodiments, the metal end is an easy-open end having aseverable panel defined by a score line in the metal layer.Alternatively, the metal end can be a sanitary end, or the metal end cancomprise a membrane sealed to an annular metal ring.

The step of forming a seam can comprise forming a crimp seam, or it cancomprise forming a double seam by rolling the curl of the metal end andthe upper end of the side wall together so as to form the upper end ofthe side wall into a body hook and to form the curl into an end hook andto interlock the body hook and the end hook.

In some embodiments the method can further comprise providing a secondheat-sealable material present on the other of (a) the lower surface ofat least the peripheral portion of the metal end and (b) the innersurface of the side wall adjacent the upper end thereof. Thus, the metalend and the side wall both have respective heat-sealable materialsthereon. The method entails placing the second heat-sealable materialand the first heat-sealable material in contact with each other at theinterface between the chuck wall and the side wall, and heating thefirst and second heat-sealable materials to a temperature sufficient tocause the first and second heat-sealable materials to be softened ormelted and to flow together, after which cooling of the first and secondheat-sealable materials is allowed to occur so as to fuse the chuck wallto the inner surface of the side wall.

The second heat-sealable material and the first heat-sealable materialcan be thermally fused together in the seam as well.

The method can further comprise the steps of filling the container witha food product prior to the step of applying the metal end to thecontainer body, and, after the interface between the chuck wall and theside wall is fused, retorting the container. During the retorting stepthe thermoplastic container body is radially unconstrained such that thecontainer body is allowed to expand radially as internal pressure isexerted on the side wall. Notably, the container body is free of anyspecial expansion panels, whereby the radial expansion of the containerbody occurs substantially uniformly about a circumference of thecontainer body.

In some embodiments, the chuck wall extends at a non-zero acute anglerelative to a longitudinal axis of the container body and is configuredsuch that a lower end of the chuck wall is smaller in diameter than theinner surface of the side wall, while an upper end of the chuck wall islarger in diameter than the inner surface of the side wall. The step ofapplying the metal end to the container body results in the side wall ofthe container body moving relatively upward from the lower end to theupper end of the chuck wall such that an interference fit is createdbetween the chuck wall and the side wall, thereby creating theintimately contacting interface therebetween.

During the induction heating step there is a substantial absence ofexternal pressure exerted to urge the chuck wall and side wall intointimate contact; rather, pressure urging the chuck wall and side walltogether comes from the interference fit that already exists betweenthem when the end is applied and seamed to the side wall. Thus, there isno need for sealing jaws to create pressure during the heating step inorder to form a secure thermal bond between the metal end and thecontainer body. Indeed, in some embodiments the heating step can becarried out with induction heating in which there can be an absence ofcontact between the induction tool and the metal end.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a diagrammatic depiction of several steps of a process formaking containers in accordance with one embodiment of the invention;

FIG. 2 is a photomicrograph of a sectioned container in the region ofthe metal end's seam with the container body, in accordance with anembodiment of the invention;

FIG. 3 is a cross-sectional view of an apparatus, along line 3-3 in FIG.4, in accordance with an embodiment of the invention, showing one stepof a method in accordance with an embodiment of the invention;

FIG. 4 is a top view of the apparatus of FIG. 3;

FIG. 5 is a view similar to FIG. 3, showing a further step of a methodin accordance with an embodiment of the invention;

FIG. 6 is a view similar to FIG. 3, but illustrating an alternativeembodiment of the invention; and

FIG. 7 is a cross-sectional view of a portion, greatly enlarged, of acontainer in accordance with an embodiment of the invention, showing thestructure of the metal end and its seam to the container body.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings in which some but not allembodiments of the inventions are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout. Thedrawings are not necessarily to scale, and thus the relative proportionsof various elements (e.g., thicknesses of layers in multi-layerstructures) suggested by the drawings is not necessarily indicative ofthe actual relative proportions.

With reference to FIG. 1, several steps of a process for makingcontainers in accordance with an embodiment of the invention areschematically depicted. In a first step, an extruder 10 is employed toextrude a substantially thermoplastic tube 12 as a continuous extrusion.The extruder 10 includes a screw 14 or the like that feeds a moltensubstantially thermoplastic material under pressure through a die 16such that the continuous tube 12 is extruded through an annular dieorifice 18. The extruded tube 12 can have a monolayer or multi-layerconstruction. As an example of a multi-layer construction, the tube wallcan have the structure (from ID to OD): heat-sealable layer/tielayer/barrier layer/tie layer/heat-sealable layer.

The tube 12 is cooled sufficiently (via known cooling means, notillustrated) and is then cut into parent tubes 20 of a convenientlength. Typically each parent tube 20 will be of sufficient length toprovide a plurality of container bodies 22 cut from the parent tube asshown.

Alternatively, in the case of metal container bodies 22, they aremanufactured according to known techniques (not shown).

Each container body 22 is then mated with a pair of metal ends 30.

The metal end 30 and container body 22 in some embodiments can beconstructed to mate with each other as described in Applicant'sco-pending application Ser. No. 13/161,713 filed on Jun. 16, 2011, theentire disclosure of which is hereby incorporated herein by reference.

The metal end 30 includes a central portion 32 and an outer peripheralportion 34 extending generally radially outwardly from the centralportion 32 and extending circumferentially about the central portion 32.The peripheral portion 34 has a radially outer part and a radially innerpart. The radially outer part defines a curl 36 having a lower surfacethat is generally concave downward in an axial direction of the metalend. The radially inner part defines a chuck wall 38 that extendsgenerally downward and radially inward from the curl 36. The chuck wall38 can be a compound-angle chuck wall, as described in the above-noted'713 application, having an upper part adjacent the curl 36 and a lowerpart joined to and positioned below the upper part. The upper part ofthe chuck wall is substantially linear and oriented relative to theaxial direction at a relatively smaller non-zero angle and the lowerpart of the chuck wall is substantially linear and oriented relative tothe axial direction at a relatively larger angle compared to the upperpart of the chuck wall.

The metal end 30 is configured such that at least a bottom edge of thelower part of the chuck wall has an outside diameter that is smallerthan the inside diameter of the container body side wall 24 at the upperedge thereof. Additionally, the chuck wall 38 is configured such that itbecomes somewhat larger in diameter than the inside diameter of thecontainer body side wall 24 as the top edge of the side wall progressesup toward the curl 36 during mate-up of the metal end 30 with thecontainer body 22. In other words, the side wall's ID is undersized inrelation to the OD of the chuck wall adjacent the curl. This has theeffect of “wiping” the inner surface of the side wall 24 with the metalend during mate-up, which has the benefit of cleaning the inner surfaceprior to seaming. This also results in an interference fit between thechuck wall 38 and the side wall 24.

Once the metal end 30 is mated with the container body 22, a seamingoperation is performed in order to seam the metal end onto the containerbody. In the illustrated embodiment, the container body is astraight-walled (non-flanged) container body, and a crimp seam 40 isformed between the metal end and the container body, in which the sidewall 24 remains substantially straight and is compressed between thechuck wall 38 and a deformed portion of the curl 36. Alternatively, inother embodiments, a double seam can be formed, in which case thecontainer body can be flanged. The crimp seam 40 has the advantage ofbeing usable with non-flanged container bodies and yet providing apositive locking of the metal end 30 onto the container body 22 evenbefore the metal end is heat-sealed to the container body. This can beseen in FIG. 2, which is a photomicrograph of a sectioned container inthe region of the crimp seam 40. A “nub” or interlocking portion of thecontainer body side wall is formed by the folded peripheral edge of thecurl “biting” into the side wall. The nub and the folded edgeeffectively interlock, thereby locking the metal end onto the containerbody.

It will be understood, of course, that a second metal end is attached tothe opposite end of the container body 22 in the same fashion describedabove. Alternatively, in the case of a container body having an integralbottom wall (as may be the case with, for example, a blow-molded,thermoformed, or injection-molded plastic container body, or adeep-drawn metal container body), the second metal end is not required.

The above-described interlocking of the metal end 30 and container body22 alone, however, may not be sufficient to enable the container towithstand a retort process in some container configurations, such aswhen the container body 22 is plastic or is a thin metal or a compositematerial. In order to be able to withstand retort intact in thoseinstances, the container is subjected to a heat-sealing operation tofuse portions of the metal end 30 to the container body side wall 24. Inthis regard, at least one of the respective surfaces of the metal endand side wall that are intimately contacting each other in the region ofthe crimp seam 40 is formed by a heat-sealable material, and the twosurfaces are such that heating of the crimp seam to soften or melt thisheat-sealable material, followed by cooling of the material, causes thetwo surfaces to be “thermally fused” to each other. More specifically,it is important to the attainment of adequate “blow-off resistance”during retort (or other high-internal-pressure condition of thecontainer) that at least the chuck wall 38 of the metal end 30 bethermally fused to the inner surface of the side wall 24 of thecontainer body, and preferably both the chuck wall 38 should bethermally fused at the ID and a portion of the curl 36 (or, moreaccurately, what was the curl prior to the seaming operation) should bethermally fused at the OD of the container body side wall 24.

The thermal fusing operation is diagrammatically depicted in FIG. 3,illustrating an induction sealer 50 that can be used in the practice ofthe invention, depicted in a diagrammatic cross-sectional view. Thesealer 50 includes a conveyor 60 comprising an endless belt 62 loopedabout a pair of spaced parallel rolls 64, 66. At least one of the rolls64, 66 is rotatably driven about its axis and in turn drives the belt62. As shown in FIG. 3, the rolls 64, 66 rotate clockwise and the belt62 thus travels clockwise such that its upper flight moves from left toright in the figure. The belt 62 supports a series of containerassemblies (each consisting of a container body 22 and a metal end 30)on the upper flight of the belt.

The container assemblies are loaded (by suitable means, not shown) ontothe conveyor 60. There is a gap between adjacent container assemblies inthe conveyance direction (i.e., the left-to-right direction in FIG. 3),as illustrated. This gap may be maintained in a uniform fashion by, forexample, configuring the belt 62 to have a series of uniformly spacedrecesses each of which receives a container assembly. The belt 62 can bea “single-lane” or “multiple-lane” belt. A single-lane belt has a singlerow of such recesses extending in the longitudinal (conveyance)direction. A multiple-lane belt has two or more such rows spaced apartwidthwise on the belt so that multiple series of container assembliescan be conveyed simultaneously through the induction sealing process.The open ends of the container bodies 22 are against the belt 62 and themetal ends 30 are located at the upper ends of the container bodies.

The apparatus 50 further includes a pressure belt 70 comprising anendless belt 72 looped about a pair of spaced parallel rolls 74, 76. Atleast one of the rolls 74, 76 is rotatably driven about its axis and inturn drives the belt 72. As shown in FIG. 3, the rolls 74, 76 rotatecounterclockwise and the belt 72 thus travels counterclockwise such thatits lower flight moves from left to right in the figure. The pressurebelt 72 is driven to travel at the same linear speed as that of theconveyor belt 62, and the pressure belt is arranged so that its lowerflight presses down on the metal ends 30 in a downward direction towardthe conveyor 60.

Disposed within the loop of (as illustrated), or adjacent to a lowerflight of (not shown), the pressure belt 72 is one or more inductionheads 80 (only one being illustrated). Each induction head comprises awire coil 84 and a ferrous core 86, depicted schematically in thefigures. The wire coil is wound in a particular configuration so as toproduce the desired electromagnetic field when an alternating electricalcurrent is passed through the wire. In particular, as known to thoseskilled in the art, the coil configuration dictates the pattern andstrength of the electromagnetic field for a given AC current. Moreparticularly, the magnetic axis A1 of the induction head 80 isschematically illustrated in FIG. 4 as being parallel to the conveyancedirection, but of course the magnetic axis can be oriented with adifferent orientation with respect to the conveyance direction. Themagnetic axis can be parallel to the plane defined by the lower flightof the pressure belt 70, or can lie in a different plane. Theillustrated orientation of the magnetic axis A1 is exemplary only, andother orientations can be used.

As each container assembly is carried on the conveyor 60 along theconveyance direction, the electromagnetic field of the induction head80, schematically illustrated by field lines EF1 in FIG. 4, induces eddycurrents through the entirety of a metal end 30 when it comes beneaththe head 80. These eddy currents heat the metal layer of the metal endand this heat is conducted to the heat-sealable thermoplastic material,causing the metal end 30 to become thermally fused to the container body22.

The container assemblies thus have the metal ends 30 sealed to the oneend of the container bodies 22 by the action of the induction head 40.As the container assemblies are conveyed beyond the induction head onthe conveyor 60, a cooling device 90 (FIG. 4) such as an air knife,water sprayer, or the like, provides cooling to the metal ends while thepressure belt 70 is still applying pressure on the metal ends to keepthem from coming off the container bodies. As noted, the pressure belt70 can be vertically adjustable, as denoted by arrow A in FIG. 3, toaccommodate containers of different heights. The pressure belt 70 actsto prevent the containers from growing in height, and thus effectivelyclamps the metal ends on the container bodies during the coolingprocess. The cooling of the ends by the cooling device 90 ensures thatthe heat-sealable thermoplastic material is solidified before thecontainers are discharged from the conveyor 60.

Container assemblies produced by the process explained above anddepicted in FIG. 3 are of course only partially completed, but are incondition to be filled with the desired contents and sealed closed. FIG.5 depicts the process of sealing the filled containers closed. After thecontainers are filled and metal ends are applied and seamed onto theopen ends, the containers are again loaded onto the conveyor 60 for asecond pass through the apparatus 50. It will be understood, of course,that the apparatus 50 of FIG. 5 may be a duplicate of the apparatus 50of FIG. 3, and may be located at a different site from that of FIG. 3.For example, at a first site, partial container assemblies, consistingof container bodies 22 closed at only one end by metal ends 30 may beproduced as in FIG. 3. These assemblies may be transported to a secondsite at which another apparatus 50 is located. At this second site, thecontainers may be filled, metal ends may be seamed onto the open ends toclose them, and then these filled containers may be loaded onto theconveyor 60 of the apparatus 50.

In the second pass through the apparatus 50 illustrated in FIG. 5, theprocess of FIG. 3 is essentially repeated to seal the metal ends 30 ontothe container bodies 22. Again, the induction head 40 heats the metalends 30 to seal them onto the container bodies, and the cooling device90 cools the metal ends before the containers are discharged from theconveyor 60.

FIG. 6 depicts an apparatus 50′ in accordance with an alternativeembodiment of the invention. The apparatus 50′ differs from theapparatus 50 previously described in that the induction head 40 islocated within the loop of (as illustrated), or adjacent to a lowerflight of (not shown), the lower belt 62 rather than the upper pressurebelt 72. With this arrangement, the product within the containers actsas a heat sink when the second metal end is induction-sealed to eachcontainer body.

In the embodiments illustrated and described above, the conveyance pathfor the workpieces is linear. The present invention, however, is notlimited to any particular conveyor configuration. For example, a rotaryconveyor (turntable, turret, etc.) can be used for conveying workpiecesand multiple induction heads can be disposed adjacent the resultingcircular conveyance path for exposing the workpieces to a plurality ofdifferently oriented electromagnetic fields, in a manner closelyanalogous to that described herein.

With reference to FIG. 7, the metal end 30 can have a metal layer 42 andan interior layer or coating of a heat-sealable material 44. Anysuitable heat-sealable material can be used for the layer 44,non-limiting examples of which include: acrylonitrile butadiene styrene(ABS), acrylic (PMMA), celluloid, cellulose acetate, cyclic olefincopolymer (COC), ethylene-vinyl acetate (EVA), ethylene vinyl alcohol(EVOH), fluoroplastics (PTFE, alongside with FEP, PFA, CTFE, ECTFE,ETFE), ionomers, liquid crystal polymer (LCP), polyoxymethylene (POM oracetal), polyacrylates (acrylic), polyacrylonitrile (PAN oracrylonitrile), polyamide (PA or Nylon), polyamide-imide (PAI),polyaryletherketone (PAEK or Ketone), polybutadiene (PBD), polybutylene(PB), polybutylene terephthalate (PBT), polycaprolactone (PCL),polychlorotrifluoroethylene (PCTFE), polyethylene naphthalate (PEN),polyethylene terephthalate (PET), polycyclohexylene dimethyleneterephthalate (PCT), polycarbonate (PC), polyhydroxyalkanoates (PHAs),polyketone (PK), polyester, polyethylene (PE), polyetheretherketone(PEEK), polyetherketoneketone (PEKK), polyetherimide (PEI),polyethersulfone (PES), chlorinated polyethylene (CPE), polyimide (PI),polylactic acid (PLA), polymethylpentene (PMP), polyphenylene oxide(PPO), polyphenylene sulfide (PPS), polyphthalamide (PPA), polypropylene(PP), polystyrene (PS), polysulfone (PSU), polytrimethyleneterephthalate (PTT), polyurethane (PU), polyvinyl acetate (PVA),polyvinyl chloride (PVC), polyvinylidene chloride (PVDC),styrene-acrylonitrile (SAN). Where the container is to beretort-processed, a suitable heat-sealable material able to withstandthe retort-processing conditions should be selected.

When the metal layer 42 is heated by induction heating, theheat-sealable layer 44 is heated by conduction, which causes theheat-sealable material to be softened or melted. Because theelectromagnetic field's strength obeys the inverse square law, Jouleheating of the metal end is greatest in the parts of the end closest tothe coil of the induction heater and decreases proportional to theinverse square of the distance from the coil. Thus, only localizedheating of the metal end occurs with a great enough magnitude to causemelting of the heat-sealable layer 44. More particularly, the melting ofthe heat-sealable layer 44 is confined essentially to the region of theseam 40.

As FIG. 7 indicates, the induction heating of the seam 40, followed bycooling (which occurs rapidly upon cessation of the electromagneticfield or movement of the container away from the coil), results in twoareas of thermal fusing between the metal end 30 and container body sidewall 24: there is an inner seal S_(i) between the inner surface of theside wall 24 and a portion of the chuck wall 38 that lies parallel toand intimately contacts the side wall, and there is an outer seal S_(o)between the outer surface of the side wall 24 and a portion of what wasthe curl of the metal end prior to seaming. The seals S_(i) and S_(o) inFIG. 7 are depicted for illustrative purposes as if they were each adistinct layer between the metal end 30 and the side wall 24, but it isto be understood that in reality the seals are formed by a melding ofthe heat-sealable layer 44 of the metal end and the thermoplasticmaterial on the surface of the side wall 24.

It is important to the attainment of adequate blow-off resistance thatthe chuck wall 38 include a portion that is parallel to and intimatelycontacting the inner surface of the side wall 24, and that this portionbe thermally fused as described above. This results in the interfacebetween the chuck wall 38 and the side wall 24 being oriented along adirection substantially parallel to the axis of the container, such thatstress on the interface caused by internal pressure inside the containerexerted on the metal end 30 is predominantly shear stress in the planeof the interface (as opposed to out-of-plane stress tending to peel onepart from the other).

It is also a feature of the present invention that during the heatingstep for thermally fusing the end 30 to the side wall 24, there is asubstantial absence of external pressure exerted on the chuck wall 38and side wall 24 for urging them together. Rather, pressure urging thechuck wall and side wall together comes from the interference fit thatexists between them, as previously described. Indeed, when an inductionheating apparatus 50 is employed as described above, there is no contactbetween the induction head and the metal end.

Various constructions of the metal end 30 and container body side wall24 can be employed in the practice of the present invention. As notedwith respect to FIG. 7, in one embodiment the metal end 30 can have aninterior heat-sealable layer 44. The container body can be metal asillustrated.

When plastic, the container body side wall 24 can be a mono-layerconstruction, and the substantially thermoplastic side wall 24 can beheat-sealable to the heat-sealable layer 44 of the metal end.Alternatively, in other embodiments, the side wall 24 can be amulti-layer plastic construction. For example, the side wall 24 cancomprise at least two layers including an interior heat-sealable layerand a barrier layer providing moisture and gas barrier properties forthe container body. The metal end 30 furthermore does not necessarilyhave to have an interior heat-sealable layer, as long as the interiorsurface is fusible to the heat-sealable layer of the side wall 24. Themetal end 30 can have a bare metal surface on its interior side. It canhave a metal layer of homogeneous construction, but it is also possiblefor the metal end to be, for example, ETP (electrolytic tin plate steel)consisting of a layer of steel to which an ultra-thin coating of tin iselectrolytically deposited, for example on the interior product-facingsurface. As an unillustrated example, the container body side wall 24can consist of five layers, in order from ID to OD: an interiorheat-sealable layer, a tie layer, a barrier layer, a tie layer, and anexterior heat-sealable layer. Any of the previously describedheat-sealable materials can be used for the heat-sealable layers. Thebarrier layer can comprise any suitable material providing the necessarybarrier properties for the particular application to which the containerwill be put. Non-limiting examples of such barrier materials includeethylene vinyl alcohol (EVOH), polyvinyl alcohol (PVOH), polyvinylidenechloride copolymer (PVDC), polyacrylonitrile (PAN), polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), liquid crystalpolymers (LCP), amorphous nylon, nylon 6, nylon 66, nylon-MXD6, and thelike. The tie layers can be any suitable adhesive materials for adheringthe heat-sealable layers to the barrier layer.

When the metal end 30 does not include a heat-sealable layer, theheat-sealable layers of the container body wall can be designed tothermally fuse to the bare metal surface so as to form the seals S_(i)and S_(o) depicted in FIG. 7. For example, an ionomer (e.g., SURLYN® orthe like) will thermally fuse to a bare metal such as ETP.

The above-described embodiments are not limiting in terms of theparticular construction of the metal end 30 and side wall 24. Thepresent invention is applicable to and includes any combination of metalend and side wall constructions in which at least one of theirrespective surfaces that are intimately contacting each other in theregion of the seam 40 is formed by a heat-sealable material, and the twosurfaces are such that heating of the seam to soften or melt thisheat-sealable material, followed by cooling of the material, causes thetwo surfaces to be “thermally fused” to each other. Additionally, aspreviously noted, it is important for at least part of the chuck wall 38to be parallel to and intimately contacting the side wall 24 so that aninterior seal S_(i) is created that is placed predominantly in shear byinternal pressure in the container such as during retort.

A further advantage of the container of the invention is its ability toundergo elastic expansion during high internal-pressure conditions suchas retort, and then return substantially to its original configurationwhen the high internal pressure is relieved. This helps alleviateinternal pressure and, consequently, the stresses exerted on the chuckwall/side wall interface and the seam. To realize this advantage, ofcourse, the container body must be relatively unconstrained so that itis able to expand radially.

The foregoing description focuses on containers having crimp-seamed andsealed metal ends. As noted, however, the invention is not limited tocrimp seaming. Alternatively, the metal ends can be double seamed andthen sealed via an induction heating or other process. part from thedifferent seam configuration, the double-seamed containers are similarto the previously described crimp-seamed containers. The double seam ischaracterized by the upper end of the side wall 24 forming a body hookand the curl of the metal end forming an end hook that is interlockedwith the body hook.

In typical double-seamed containers, a seaming compound is often appliedto the metal end in the region of the curl. The seaming compound flowsduring double seaming so as to fill up any gaps that may exist betweenthe metal end and container body wall in the seam area. Containers inaccordance with the invention can be made either with our withoutconventional seaming compounds.

In the foregoing description and the appended claims, references to thecontainer body being “substantially thermoplastic” or the like mean thatthermoplastic is the majority ingredient of the container body on avolume basis, and furthermore that any non-thermoplastic ingredient(s)does (do) not impair the ability of the container body to be heat-sealedto a metal end or to expand elastically during retort processing aspreviously described. For example, a substantially thermoplasticcontainer body can include non-thermoplastic ingredients such aspigments (e.g., titanium dioxide), dyes, or other additives forimparting visual characteristics (e.g., coloration, opacity, etc.) orother properties not provided by the thermoplastic itself. As anotherexample, a container body of composite construction such aspaper/thermoplastic or metal/thermoplastic would not be “substantiallythermoplastic” (even if the thermoplastic were the majority ingredientby volume) if the paper or metal component impaired the ability of thecontainer body to be heat-sealed to a metal end and/or to expandelastically during retort processing.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. A method of making a hybrid metal/plastic retortcontainer, comprising the steps of: providing a container body having aside wall extending about a container body axis, the side wall having alower end and an upper end, the upper end defining an upper edge thatextends about a top opening of the container body, the side wall havingan inner surface and an outer surface; applying a metal end to the upperend of the container body, the metal end having at least a metal layerand comprising a central portion and an outer peripheral portionextending generally radially outwardly from the central portion andextending circumferentially about the central portion, the peripheralportion having a radially outer part and a radially inner part, a firstheat-sealable material being present on at least one of (a) a lowersurface of at least the peripheral portion of the metal end and (b) theinner surface of the side wall adjacent the upper end thereof, theradially outer part of the peripheral portion defining a curl, theradially inner part of the peripheral portion defining a chuck wall thatextends generally downward from the curl and has a radially outersurface forming an interface with the inner surface of the side wall ofthe container body; forming a seam connecting the metal end to the upperend of the side wall, the seam having the curl of the metal end and theupper end of the side wall interlocked, the container body and seamedmetal end constituting a container assembly; disposing the containerassembly between a lower conveyor and an upper pressure belt whichcooperatively engage opposite ends of the container assembly to preventthe metal end from coming off the container body, and which convey thecontainer assembly along a path; and induction heating the metal end tomelt the first heat-sealable material and then cooling the firstheat-sealable material so as to fuse the metal end onto the containerbody, wherein the heating and cooling steps take place during theengagement of the conveyor and pressure belt with the containerassembly.
 2. The method of claim 1, wherein the step of forming a seamcomprises forming a crimp seam.
 3. The method of claim 1, wherein thestep of forming a seam comprises forming a double seam by rolling thecurl of the metal end and the upper end of the side wall together so asto form the upper end of the side wall into a body hook and to form thecurl into an end hook and to interlock the body hook and the end hook.4. The method of claim 1, further comprising providing a secondheat-sealable material present on the other of (a) the lower surface ofat least the peripheral portion of the metal end and (b) the innersurface of the side wall adjacent the upper end thereof, and wherein:the second heat-sealable material and the first heat-sealable materialare placed in contact with each other at the interface between the metalend and the side wall, and the first and second heat-sealable materialsare heated to a temperature sufficient to cause the first and secondheat-sealable materials to be softened or melted and to flow together,after which cooling of the first and second heat-sealable materials isallowed to occur so as to fuse the metal end to the side wall.
 5. Themethod of claim 1, further comprising the steps of: filling thecontainer with a food product prior to the step of applying the metalend to the container body; and after the metal end is fused to the sidewall, retorting the container.
 6. The method of claim 5, wherein thecontainer body is substantially thermoplastic and during the retortingstep the thermoplastic container body is radially unconstrained suchthat the container body is allowed to expand radially as internalpressure is exerted on the side wall, thereby reducing pressure build-upwithin the container and consequently the stress placed upon the sidewall and metal end.
 7. The method of claim 6, wherein the container bodyis free of any special expansion panels, whereby the radial expansion ofthe container body occurs substantially uniformly about a circumferenceof the container body.
 8. The method of claim 1, wherein the chuck wallextends at a non-zero acute angle relative to a longitudinal axis of thecontainer body and is configured such that a lower end of the chuck wallis smaller in diameter than the inner surface of the side wall, while anupper end of the chuck wall is larger in diameter than the inner surfaceof the side wall, and wherein the step of applying the metal end to thecontainer body results in the side wall of the container body movingrelatively upward from the lower end to the upper end of the chuck wallsuch that an interference fit is created between the chuck wall and theside wall.
 9. The method of claim 8, wherein during the inductionheating step there is a substantial absence of external pressure exertedon the chuck wall and side wall, pressure between the chuck wall andside wall coming rather from said interference fit.